The UK Government is committed by their 2003 Energy White Paper to developing a sustainable energy economy in the 21st Century, and to taking a lead in reducing CO2 emissions amongst the industrialised (OECD) countries. A target of reducing these emissions to 60% of their existing figure by 2050 has been adopted. The only way in which this fall could be achieved is by significantly reducing primary energy consumption to between 45% and 75% of the present demand; depending on the energy technology mix. This requires the widespread adoption of energy-saving measures across the economy. It is in this area that thermodynamic analysis can make a major contribution to identifying where the improvement potential lies. Energy options are inevitably constrained by thermodynamic limits on individual plant and the sector as a whole. Nevertheless, energy policy advice to Governments, particularly that in the UK, tends to be dominated by views from the humanities and social sciences. Thermodynamic ideas, by contrast, often appear rather esoteric to the non-specialist; this dichotomy is arguably a manifestation of C.P. Snow's 'two cultures' (the apparent divide between the arts and social sciences on the one hand, and engineering and the natural sciences on the other). Other methods for generating policy advice, including that from the discipline of economics, will not provide substitute insights to those of energy and exergy analysis. However, thermodynamic techniques such as these should not be used alone, but as part of a broader interdisciplinary 'toolkit' of sustainability assessment methods. They cannot determine, for example, the economic consequences or the environmental (ecotoxicological) impact of different energy technologies. (C) 2003 Elsevier Ltd. All rights reserved.